This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2000-054487, filed Feb. 29, 2000; and No. 2000-224271, filed Jul. 25, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to a dielectric leaky-wave antenna and, more particularly, to a dielectric leaky-wave antenna for leaking electromagnetic waves from an electromagnetic wave transmission guide formed by a ground plane and dielectric, in which the structure is simplified and a technique of increasing the efficiency is adopted.
In recent years, demands have arisen for an antenna which can be used in the milliwave band for a radio LAN, a radar mounted on an automobile, or the like.
As the milliwave-band antenna, various antennas are proposed, including an antenna which leaks electro-magnetic waves from a slot formed in a waveguide, and a so-called triplate antenna in which a coupling slot is formed in a slab and power is fed via a triplate line.
Of these antennas, the antenna using a waveguide is difficult to manufacture because of a three-dimensional structure partitioned by a metallic wall.
The triplate antenna has a large line loss though the line loss is smaller than that of a microstrip line. Further, unwanted waves generated by reflection of an element are transmitted through the triplate line, so the antenna efficiency is low.
To solve these problems, a parallel-plate slot array antenna is proposed in which a transmission guide equivalent to a waveguide is formed by upper and lower metallic surfaces of a printed board and through holes extending through the metallic surfaces (TECHNICAL REPORT OF IEICE.A. PP. 99-114, RCS99-111 (1999-10)).
However, the parallel-plate antenna in which a transmission guide equivalent to a waveguide is formed using through holes in a printed board is more complicated in structure than a dielectric leaky-wave antenna, and requires a high manufacturing cost for forming through holes.
Further, this antenna uses a uniform electromagnetic field, i.e., TEM mode in a section perpendicular to the propagation direction. Thus, strong currents equal in magnitude flow through upper and lower metallic plates to generate a conductor loss, which increases the loss.
A dielectric plate is actually inserted between parallel plates in order to shorten the waveguide wavelength and suppress the grating lobe, too. This also generates a dielectric loss to limit a decrease in loss.
As another type of antenna, a leaky-wave antenna is proposed in which a narrow radiation dielectric bar is arranged as a transmission line on a two-layered dielectric slab, the height of part of the dielectric bar is changed, and metallic strips are periodically laid out at a small-height portion (U.S. Pat. No. 4,835,543, xe2x80x9cDielectric slab antennasxe2x80x9d). This antenna is a one-dimensional array antenna. To obtain a two-dimensional plane antenna important in practical use, a plurality of radiation dielectric bars must be aligned, which results in low mass productivity. In addition, a feed system for feeding power to these dielectric bars in phase is complicated.
Furthermore, an invention has been applied in which a dielectric slab having projections on a plate in the vertical direction is prepared, and the surface of the slab is metallized to form a continuous transverse stub, and the stub is used for an antenna (U.S. Pat. No. 5,266,961, xe2x80x9cContinuous transverse stub element devices and methods of making samexe2x80x9d). This antenna is a slot array antenna uniform in the transverse direction using a parallel-plate waveguide to which a dielectric is inserted. In general, a dielectric material such as alumina having a high frequency such as a milliwave and a low loss is difficult to process. The manufacture of a complicated dielectric slab having many projections is disadvantageous in cost.
For this reason, implementation of an antenna having a high antenna efficiency and simple structure is demanded.
It is an object of the present invention to provide a dielectric leaky-wave antenna for leaking electromagnetic waves from an electromagnetic wave transmission guide formed by a ground plane and dielectric, in which the structure is simplified and a technique of increasing the antenna efficiency is adopted to meet this demand.
To achieve the above object, according to the present invention, (1) there is provided a dielectric leaky-wave antenna comprising:
a ground plane;
a dielectric slab arranged on one surface of the ground plane to form a transmission guide for transmitting an electromagnetic wave along a surface from one end to the other end between the dielectric slab and the ground plane;
a perturbation loaded on the dielectric slab to leak the electromagnetic wave from the surface of the dielectric slab;
a feed for supplying the electromagnetic wave to one end of the transmission guide formed by the ground plane and the dielectric slab; and
a dielectric layer which is interposed between the ground plane and the dielectric slab and has a lower permittivity than a permittivity of the dielectric slab.
According to the present invention, (2) there is provided a dielectric leaky-wave antenna defined in (1), characterized in that the dielectric layer includes a gas layer including air or a vacuum layer.
According to the present invention, (3) there is provided a dielectric leaky-wave antenna defined in (1), characterized in that the perturbation is formed from a metallic strip or slot perpendicular to an electromagnetic wave transmission direction of the transmission guide.
According to the present invention, (4) there is provided a dielectric leaky-wave antenna defined in (1), characterized in that the perturbation is formed from a metallic strip or slot having an angle of 45xc2x0 with respect to an electromagnetic wave transmission direction of the transmission guide.
According to the present invention, (5) there is provided a dielectric leaky-wave antenna defined in (1), characterized in that the perturbation is formed from a pair of metallic strips or pair of slots which form an angle of 90xc2x0 with each other, and is loaded on the dielectric slab so as to form an angle of 45xc2x0 with respect to an electromagnetic wave transmission direction of the transmission guide by each metallic strip of the pair of metallic strips or each slot of the pair of slots.
According to the present invention, (6) there is provided a dielectric leaky-wave antenna defined in (1), characterized in that a pair of perturbations parallel-arranged at an interval almost xc2xc a wavelength of the electromagnetic wave in the transmission guide in the electromagnetic wave transmission direction of the transmission guide are loaded at a predetermined interval in the electromagnetic wave transmission direction of the transmission guide.
According to the present invention, (7) there is provided a dielectric leaky-wave antenna defined in (6), characterized in that one of the pair of perturbations is formed on one surface of the dielectric slab, and the other is formed on an opposite surface of the dielectric slab.
According to the present invention, (8) there is provided a dielectric leaky-wave antenna defined in (6), characterized in that the pair of perturbations are formed on an upper surface of the dielectric slab.
According to the present invention, (9) there is provided a dielectric leaky-wave antenna defined in (1), characterized in that
the feed is formed to radiate a cylindrical wave, and
a wave-front conversion section for converting the cylindrical wave radiated by the feed into a plane wave and guiding the plane wave to the transmission guide is arranged at one end of the dielectric slab.
According to the present invention, (10) there is provided a dielectric leaky-wave antenna defined in (1), characterized in that the wave-front conversion section is formed by extending the dielectric slab toward the feed.
According to the present invention, (11) there is provided a dielectric leaky-wave antenna defined in (10), characterized in that a matching section for matching the feed and the wave-front conversion section and guiding the electromagnetic wave supplied by the feed to the wave-front conversion section is arranged at a distal end of the wave-front conversion section.
According to the present invention, (12) there is provided a dielectric leaky-wave antenna defined in (10), characterized in that
the feed is formed to transmit an electromagnetic wave input from one end to one end of the dielectric slab along the ground plane and to radiate the electromagnetic wave from an aperture at the other end that is formed to surround an edge of the one end of the dielectric slab, and
a matching section projecting toward the ground plane so as to decrease a gap between the feed and a surface of the wave-front conversion section stepwise or continuously toward the wave-front conversion section in order to match the feed and the wave-front conversion section is arranged in the aperture at the other end of the feed.
According to the present invention, (13) there is provided a dielectric leaky-wave antenna defined in (9), characterized in that
the wave-front conversion section has a reflecting wall for converting a cylindrical wave into a plane wave and reflecting the plane wave, and is arranged to make one half of the reflecting wall face one end of the dielectric slab, and
the feed is arranged on a side opposite to the dielectric slab via the ground plane while a radiation surface faces the other half of the reflecting wall of the wave-front conversion section so as to radiate an electromagnetic wave toward the other half.

According to the present invention, (14) there is provided a dielectric leaky-wave antenna defined in (13), characterized in that a matching section for matching the wave-front conversion section and the transmission guide of the dielectric slab is arranged at one end of the dielectric slab.
According to the present invention, (15) there is provided a dielectric leaky-wave antenna defined in (11), characterized in that the matching section is tapered to decrease a thickness toward an electro-magnetic wave input side.
According to the present invention, (16) there is provided a dielectric leaky-wave antenna defined in (14), characterized in that the matching section is tapered to decrease a thickness toward an electro-magnetic wave input side.
According to the present invention, (17) there is provided a dielectric leaky-wave antenna defined in (11), characterized in that the matching section is formed from a dielectric having a permittivity different from a permittivity of the dielectric slab.
According to the present invention, (18) there is provided a dielectric leaky-wave antenna defined in (14), characterized in that the matching section is formed from a dielectric having a permittivity different from a permittivity of the dielectric slab.
According to the present invention, (19) there is provided a dielectric leaky-wave antenna defined in (13), characterized in that
the wave-front conversion section is formed to transmit an electromagnetic wave reflected by the reflecting wall to one end of the dielectric slab along the ground plane and to radiate the electromagnetic wave from an aperture at the other end that is formed to surround an edge of the one end of the dielectric slab, and
a matching section projecting toward the ground plane so as to decrease a gap between the feed and a surface of the dielectric slab stepwise or continuously toward the dielectric slab in order to match the wave-front conversion section and the transmission guide of the dielectric slab is arranged in the aperture at the other end of the wave-front conversion section.
According to the present invention, (20) there is provided a dielectric leaky-wave antenna defined in (9), characterized in that
the feed has a plurality of radiators having different radiation center positions, and
the wave-front conversion section converts a cylindrical wave radiated by each radiator into a plane wave whose wave front is inclined at an angle corresponding to the radiation center position of the each radiator, and supplies the plane wave to the transmission guide.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.